THE LABYRINTH AND THE EIGHTH NERVE
rule both the cochlear and vestibular apparatus are affected. Sometimes the
cochlear apparatus alone is involved; rarely do we have a more or less
isolated affection of the vestibular apparatus. The pathological changes
producing the deafness may be: (1) Hydrocephalus. (2) Changes in the walls
Fig. 205. Meningitic neurolabyrinthitis. Pus is invading the cochlea along the branches of the cochlear
nerve from the internal meatus. 1, Purulent exudate in helicotrema; 2, Exudate in scala vestibuli; 3,
Same in scala tympani; 4, Cochlear nerve with haemorrhagic purulent exudate around; 5, Endosteum
detached from wall of scala tympani of basal coil (artefact).
Fig. 206. Meningitic neurolabyrinthitis following pneumonia. I, Purulent exudate in scala vestibuli—to
the left it is lying on the upper surface of Reissner's membrane; 2, Spiral ganglion infiltrated with pus;
3, Scala tympani full of pus; 4, Cochlear canal with fibrinous and slightly purulent exudate.
of the fourth ventricle. (3) Purulent infiltration of the eighth nerve, with
subsequent descending neuritis accompanied by atrophy of the spiral gan-
glion. (4) Purulent labyrinthitis (Figs. 205, 206) which, if the patient lives
long enough, is followed by the formation of granulation tissue and, later,